Method of supplying liquid

ABSTRACT

A method of supplying liquid is provided, including the steps of providing, at a first location, a cistern on land for liquid; providing, at a second location, a floating flexible container of liquid; and incrementally conveying liquid from the container to the cistern according to a demand determined according to the use of liquid in the cistern. The invention is directed to an apparatus for supplying liquid employing the on-land cistern and floating flexible container.

The present invention concerns a method of supplying liquid, and inparticular to a method of supplying water.

For certain land areas, for example parts of Greece, water is generallyscarce and has to be brought into the area from elsewhere. For coastalareas, this is commonly accomplished by shipping in water by tanker. Onarrival of the tanker, its hold of water is pumped into a nearbyon-shore cistern. In this regard, the timing of the tanker's arrival hasto be carefully managed since such on-shore cisterns are generally of acritical size. That is to say, the water in the cistern can not beallowed to run out, since such a shortage or lack of water could bedisastrous for the local inhabitants. Furthermore, because of a lack ofavailable on-shore space, such cisterns are generally restricted insize. Thus if the cistern still contains more than a certain amount ofwater on arrival of the tanker, ten it may not be able take all thetanker's cargo so that when the tanker leaves it has to carryundischarged water with it to its next destination. Since a tanker ismost cost effective when transporting goods, it is not commerciallyexpedient to wait for the cistern level to drop to enable completeemptying of the cargo. In addition, the water must be pumped into thecistern quickly since a stationary tanker does not repay the capitalinvestment therein.

Whilst careful management can help to reduce such wastage, fluctuationsin demand, for example, because of variable weather conditions, canupset predictions of water requirements. The smaller the on-shorecistern and the greater the lead time of delivery of water, the moredifficult such management becomes. For example, a small cistern will runout more quickly and will thus be affected more seriously by demandfluctuations. Also, with long delivery lead times additionalconsideration has to put into planning for future demand since shortnotice top-ups on extra demand are not possible.

An object of the present invention is to provide a method of supplyingwater that seeks to alleviate the problems associated with knownarrangements.

According to a first aspect of the present invention, there is provideda method of supplying liquid comprising the steps of:

providing at a first location a cistern on land for liquid;

providing at a second location a floating flexible container of liquid;

incrementally conveying liquid from the container to the cisternaccording to a demand determined according to the use of liquid in thecistern.

With such a method, a large flexible container of, for example, watercan be provided off-shore and connected to a cistern by way of suitablepiping. Water can be then be pumped to the cistern when usage of waterin the cistern is such that the cistern requires topping up.

The provision of a large flexible container of liquid off-shore isadvantageous in that no on-shore space is taken up, hence the size ofthe container is not restricted.

Such flexible containers are also a small fraction of the cost ofconventional tankers and hence represent a comparatively low capitalinvestment.

The use of a container in the sea is furthermore beneficial in warmclimates in that the temperature of the sea-water will keep the liquidsacred within the container cool and thus slow down deteriorationthereof.

The flexible container in question may be a floating flexible vessel ofthe sort used for transporting fluent cargo through liquid. Vessels ofthis nature take the form of closed flexible tubular or envelopestructures, generally of a synthetic rubberised fabric. Such vessels areused to transport fluent cargoes having a specific gravity less thanthat of seawater. When laden the vessel is virtually submerged andbuoyancy is supplied by the cargo. To move such laden vessels, they aretowed from one end, for example, by a tug boat. Such vessels are muchcheaper than conventional tankers.

With the present invention, the use of a floating flexible vessel as astorage means on a semi-permanent basis offers advantages in that such avessel can be towed to the required location and left there untilultimately it is emptied as the contents thereof are gradually used up.The tug boat that towed the vessel to its location has a relativelyquick turn around time as compared with a tanker in that no pumping outof liquid is required. The vessel can merely be uncoupled from the tugand suitably anchored or moored, whereupon the tug can leave to completea further task.

Preferably, the method further comprises the step of replacing asubstantially empty container with a laden container. The tug may thusoperate to replace a laden vessel for an empty vessel so that its returnjourney is not wasted.

In preferred embodiments, the method further comprises pumping liquidfrom the flexible container to the cistern using a pumping meansprovided on a movable buoy. In this respect, it is relatively difficultand thus expensive to suck liquid from a container over long distances.It is however relatively easy and hence cheap to drive or push liquidaway from the same pump. Thus a pump that may be expensive to run insucking liquid over a distance of 8 meters may be relatively cheap torun in pushing liquid a distance of over 2 kilometers. Hence, where thecontainer is anchored more than a certain critical distance from shore,pumping the liquid using a pump on a movable buoy that can be broughtclose to the container can be highly effective.

According to a second aspect of the present invention there is providedapparatus for supplying liquid, such

an on land cistern for holding liquid and located at a first location;

a floating flexible container for holding liquid and located at a secondlocation;

means for conveying liquid from the container to the cistern; and

control means for determining the extent of use of liquid in the cisternand varying the quantity of liquid supplied to the cistern from thecontainer in increments according to a demand determined by the extentof said use of liquid.

With such apparatus, one can operate the method as defined above andbenefit from the advantages thereof.

Preferably, the flexible container is a floating flexible vessel of thesort used for transporting fluent cargo through liquid. The use of afloating flexible vessel offers certain advantages as discussed above.

In preferred embodiments, the apparatus further comprises a pumpingmeans for pumping liquid from the flexible container to the cistern, thepumping means being provided on a movable buoy. The movable pumpingmeans can be brought close to the flexible container so as to facilitatethe conveyance of liquid to the cistern.

Conveniently, one or more additional flexible containers can beremovably coupled with the flexible container to increase the capacityof the apparatus for periods of increased demand, for example during thesummer period.

The cistern may be a buffer cistern for covering change overs offlexible containers, the liquid being supplied direct therefrom to amains supply pump. Alternatively, the cistern is preferably a firstcistern that supplies a remotely located second cistern. The secondcistern is in this respect usually provided at an elevated position fromthe first cistern so as to provide the head required for a pressurizedwater system.

An example of the present invention will now be described by way ofreference to the accompanying drawing which shows a floating flexiblecontainer 1 in a harbour 15 coupled via a pump 2 on a movable floatingbuoy to a first on-shore cistern 3.

The pump 2 on the movable buoy may be used if the container ispositioned more than a certain critical distance from the cistern, sincesucking liquid for distances greater than this is expensive. If howeverthe container can be moored sufficiently close to the first cistern 3,then the pump 2 may be provided at the first cistern itself.

The first cistern 3 is shown supplying a remotely located second cistern4 using pump 5. The second cistern is in this respect provided at anelevated position from the first cistern so as to provide the headrequired for a pressurized water system. In this connection, the secondcistern is relatively large compared with the first cistern, althoughthis is not necessarily so.

The first cistern has a first control means 6 for determining the extentof use of liquid therefrom. The first control means further controls theconveyance of liquid from the flexible container 1 to the first cistern,for example by varying the operation of the pump 2 and/or suitablevalves between the container and the first cistern, according to theextent of use of liquid from the first cistern.

The second cistern 4 has a second control means 7 for determiningwhether the amount of water it holds falls below a minimum value. Ifthis happens then the second control means instructs the pump 5 toconvey water to the second cistern 4 from the first cistern 3.

Hence, in use of the apparatus, the flexible container carrying, forexample, water is towed and moored to a location off-shore and connectedto the first cistern by way of suitable piping. The first cisternsupplies water to a second elevated cistern if the level of water in thesecond cistern drops below a certain critical level.

As water leaves the first cistern to the second cistern, its level willdrop so that at a certain predetermined point, e.g. below 50% capacity,water will be puffed from the floating flexible container to the firstcistern as controlled by the control means 6.

Since the flexible container of water is off-shore, no significanton-shore space is taken up and the size of the container is not limitedby any on-shore restrictions. Indeed, for periods of extra demand, forexample during the summer months, one or more additional containers maybe coupled to the first cistern.

The naturally low temperature of the sea-water will keep the waterstored within the container cool and thus slow down deteriorationthereof. By using floating flexible vessels of the sort used fortransporting fluent cargo through liquid, they can be readily towed tothe required location and left there until substantially empty. The tugboat that towed the vessel to its location has thus a relatively quickturn around time as compared with a tanker in that no pumping out ofliquid is required. The vessel can merely be uncoupled from the tug andsuitably anchored, whereupon the tug can leave to complete a furthertask. The tug may thus operate to replace a laden vessel for an emptyvessel so that its return journey is not wasted.

It will be understood that the embodiment illustrated shows anapplication of the invention in one form only for the purposes ofillustration. In practice, the invention may be applied to manydifferent configurations, the detailed embodiments being straightforwardfor those skilled in the art to implement.

For example, rather than the first cistern being connected to a secondcistern, the first cistern may be a buffer cistern for covering changeovers of flexible containers, the liquid being supplied direct therefromto a mains supply pump.

Also, whilst the example described has been in relation to the supply ofpotable water, other liquids may be thus supplied, for example oil.

What is claimed is:
 1. A method of supplying liquid comprising the stepsof:providing at a first location a cistern on land for liquid; providingat a second location a floating flexible container of liquid;incrementally conveying liquid from the container to the cisternaccording to a demand determined according to the use of liquid in thecistern.
 2. A method according to claim 1, wherein the flexiblecontainer is a floating flexible vessel.
 3. A method according to claim1, further comprising the step of replacing a substantially emptycontainer with a laden container.
 4. A method according to claim 1,further comprising the step of pumping liquid from the flexiblecontainer to the cistern using a pumping means provided on a movablebuoy.
 5. A method according to claim 2, further comprising the step ofreplacing a substantially empty container with a laden container.
 6. Amethod according to claim 2, further comprising the step of pumpingliquid from the flexible container to the cistern using a pumping meansprovided on a movable buoy.
 7. A method according to claim 3, furthercomprising the step of pumping liquid from the flexible container to thecistern using a pumping means provided on a movable buoy.
 8. Apparatusfor supplying liquid comprising:an on land cistern for holding liquidand located at a first location; a floating flexible container forholding liquid and located at a second location; means for conveyingliquid from the container to the cistern; and control means fordetermining the extent of use of liquid from the cistern and varying thequantity of liquid supplied to the cistern from the container inincrements according to a demand determined by the extent of said use ofliquid.
 9. Apparatus according to claim 8, wherein the flexiblecontainer is a floating flexible vessel.
 10. Apparatus according toclaim 8, wherein the apparatus further comprises a pumping means forpumping liquid from the flexible container to the cistern, the pumpingmeans being provided on a movable buoy.
 11. Apparatus according to claim8, wherein one or more additional flexible containers can be removablycoupled with the flexible container to increase the capacity of theapparatus for periods of increased demand.
 12. Apparatus according toclaim 8, wherein the cistern is a first cistern that supplies a remotelylocated second cistern.
 13. Apparatus according to claim 9, wherein theapparatus further comprises a pumping means for pumping liquid from theflexible container to the cistern, the pumping means being provided on amovable buoy.
 14. Apparatus according to claim 9, wherein one or moreadditional flexible containers can be removably coupled with theflexible container to increase the capacity of the apparatus for periodsof increased demand.
 15. Apparatus according to claim 10, wherein one ormore additional flexible containers can be removably coupled with theflexible container to increase the capacity of the apparatus for periodsof increased demand.
 16. Apparatus according to claim 9, wherein thecistern is a first cistern that supplies a remotely located secondcistern.
 17. Apparatus according to claim 10, wherein the cistern is afirst cistern that supplies a remotely located second cistern. 18.Apparatus according to claim 11, wherein the cistern is a first cisternthat supplies a remotely located second cistern.